Several techniques are presently known for the decarbonization protection of metallic surfaces (particularly those of ferrous materials) during heat treatment of such materials. In one arrangement of this type, a coating of borax is placed directly on the surface to be protected, and serves during the heat treatment to form accelerated scaling on such surface. When the scale is removed, the exposed surface is relatively free of decarbonizing.
An additional arrangement, which is in some respect superior to the borax treatment, employs as the coating material a ceramic frit which has a high concentration of boron oxide or the like. It has been found that such substance provides a more highly viscous and adherent film on the relevant surface than does borax.